Egg pasta dough:500 g (1 lb) strong plain flourgood pinch of salt4 eggs1 teaspoon olive oil1-2 tablespoons water1. To make the pasta dough, sift the flour and salt into a bowl. Make a hollow in the centre, drop in the eggs and oil. Draw the flour into the centre, add 1-2 tablespoons of water if the mixture is too dry - the finished dough should be fairly firm to the touch. Knead the dough until smooth and elastic; this is essential if the dough is to roll properly. Wrap the dough closely and leave to rest for a minimum of 15 minutes and a maximum of 2 hours.2. Working quickly, roll out the dough with a rolling pin, giving the dough a quarter turn between each roll, until it measures 20-23 cm (8-9 inches) in diameter. Now work on the dough, rolling and stretching it until it is paper thin and has been stretched to a square measuring about 40-45 cm (16-18 inches). Cut out 6 cm (2 1/2 inch) rounds.3. For the filling, fry the onion and garlic gently in the oil until soft and lightly coloured. Add the mushrooms, continue to cook gently until the mushrooms are soft and any liquid has evaporated. Remove from the heat, beat in the ricotta cheese and egg and sufficient breadcrumbs to give a firm mixture. Season. Place a little mixture on each dough round, brush around the edge with cold water, fold over and seal to make half-moon shapes.4. Cook a few ravioli at a time for 4-5 minutes in salted boiling water. They are cooked when they rise to the surface. Remove with a slotted spoon, drain well and place in a serving dish. Cover and keep hot until all the ravioli are cooked. Just before serving, heat the butter in a pan until it is a light golden brown and pour immediately over the ravioli. Sprinkle a little of the Parmesan over and serve the rest separately. Serve the ravioli hot.